Quantitative approach to reservoir characterisation of thin-bedded turbidites: the lateral connectivity perspective

In fields producing from turbidite reservoirs, the impact of sedimentary heterogeneities on fluid flow cannot be overemphasised. However, quantifying these heterogeneities and predicting their distribution is far from being an... [ view full abstract ]

In fields producing from turbidite reservoirs, the impact of sedimentary heterogeneities on fluid flow cannot be overemphasised. However, quantifying these heterogeneities and predicting their distribution is far from being an easy task, especially in hydrocarbon reservoirs where facies variation is a significant contributing factor to reservoir complexity. The failure to adequately take account of such complexities in estimating sedimentary heterogeneities frequently results in failure to optimise production and bypassed fluids in low-pay sands.

Lateral continuity and connectivity of reservoir facies are one of the high-ranking heterogeneities that are often difficult to predict, particularly in a succession of thin-bedded turbidites (TBT). In fact, they are often consistently underestimated during field development planning. Consequently, we propose Lateral Connectivity Index (LCI), derived from the relationship between regularity of stratification and lateral continuity of beds in a particularly traceable TBT package. The attribute index is an important discriminator that varies for different deepwater architectural elements, and can be applied as a predictive tool to quantify lateral connectivity of TBT facies packages at inter-well spacing in addition to its application in modeling properties of TBT facies and associated deepwater elements.

For direct application, we collected qualitative and quantitative data from a selected basin-plain turbidite succession in the Basque-Cantabrian Basin, Northern Spain. Results analysed reveal seven packages (A-G), within two positions with 100 m spacing. For a three-dimensional study, the two positions were used to construct two pseudo-wells, and the packages were analysed in the context of their sedimentary attributes using a 3-phase workflow. The resulting attribute models were up-scaled, and subsequently conditioned to the LCI.

Results obtained by comparing the conditioned and unconditioned up-scaled models reflect a consistent relationship between LCI and net-to-gross (NTG). It is observed that lithofacies distributions are directly related to lateral connectivity of the seven TBT packages. The conditioned models indicate that LCI decreases with bed thickness, but appears to be beyond the influence of NTG. The results, however, are only valid for basin-plain turbidites and further work will centre on testing the approach for TBT packages in other deepwater architectural elements for an overall robust quantitative characterisation of TBT facies and facies associations.